Mutualistic relationships reciprocally provide benefits between species, but dissolution of the mutualisms could be advantageous in the environment where the relationship is unnecessary. About 75% of lycaenid species rely on ants to protect from natural enemies. These myrmecophilous larvae give ants nectar as rewards for the protection, thus keeping the relationships in an enemy-free space results in the exceedance of the cost over the benefit. In this study, we focus on a lycaenid buttuerfly, Arhopala japaonica, and clarify whether larvae reduce their dependence in an enemy-free space. A. japonica had been distributed mainly in the western part of Japan, but they recently expand their range to the northern part of the Honshu island. A. japonica larvae in the western Japan were parasitized by a single dominant braconid species, but no larvae were parasitized in the northern limited, Sendai City. The percentage of ant attendance in Sendai was significantly lower than that in the western population. In laboratory experiments, the percentages of ant attendance and of nectar secretion were significantly lower in the Sendai population than that of the western population. These results suggest that the A. japonica larvae in the enemy-free space indeed reduce the dependence on ants.